1. Field of the Invention
This invention relates generally to automotive windshield wiper systems. In particular, the present invention is concerned with a mechanism for varying the blade tip force of a wiper arm.
2. Description of the Related Art
Conventional windshield wiper systems typically have a drive shaft, a head mounted on the drive shaft for unitary rotation therewith, a wiper arm pivotally mounted on the head at a first end and retaining a wiper blade at a second end, and a spring between the head and wiper arm pivoting the wiper arm to press the blade against the windshield. The spring generally produces a near constant force on the wiper arm urging the blade toward the windshield.
It is desirable to vary the tip force on a windshield wiper blade to reduce chatter, blade set, wind-lift, system noise, and improve wipe quality at high vehicle speeds. Furthermore, it is desirable to selectively vary the tip force dependent on vehicle operating conditions. Conventional devices so doing typically require a dedicated rotary electric motor to displace an end of the spring in a direction providing a desired increase or decrease of spring force on the wiper arm.